An all-day Earth Day rally and concert Saturday drew some big names to the National Mall in Washington and into the world of politics to confront the dual issues of climate change and poverty.

Usher, Mary J. Blige, Gwen Stefani, Common, Fall Out Boy and Train performed at the free Global Citizen 2015 Earth Day rally hosted by rapper/entrepreneur will.i.am and journalist Soledad O'Brien. The event drew a crowd of thousands near the Washington Monument.

The rally is a joint initiative with the Global Poverty Project, which is live-streaming the event, to end extreme poverty. Organizers are seeking to highlight the problems of poverty and climate change around the world. They are also encouraging participants to commit to making environmentally friendly "acts of green" this year, and asking attendees to sign petitions for a U.N. conference on climate change planned for Paris in December.

"Whether it's the big migrations we expect to see or soil depletion or emptying the oceans, loss of species, loss of timberland — all these things are creating poverty at the same time that they are also creating climate change issues," said Kathleen Rogers, Earth Day Network president. “Eliminating poverty will require solving climate change.”

Usher performed on crutches because of a fractured foot but drew big cheers, singing his hits "Yeah!'' and "OMG'' and teaming up with Common to sing the beginning of "Glory,'' the Oscar-winning song from the movie "Selma.''

"To end poverty, it starts, in my opinion, with an education about it,'' Usher told the crowd. "I want you to go and investigate for yourself so that you can really understand what's going on.''

Backstage before his performance, Train frontman Patrick Monahan said he didn't know much before about the environmental movement and the push to end extreme poverty. But now he wants to stay involved permanently.

"It's about all of us being aware but getting our hands dirty, because it's not going to be an easy thing,'' Monahan said. ``Whatever I can do to help legislation change, which is a humongous thing, and to get dollars to go to different places.''

Monahan said he's been inspired by the charitable work of Coldplay's Martin and Hugh Evans of the Global Poverty Project, which has set a goal to end extreme poverty by 2030.

Earth Day organizers also announced plans with developers of the popular "Angry Birds" game to create a new in-game experience about climate change. "Angry Birds" has been downloaded 2.8 billion times worldwide. The game's climate change campaign will coincide with the U.N. General Assembly in September as world leaders tackle sustainability goals.

Earth Day is officially observed on April 22. This year marks Earth Day's 45th anniversary.

Earlier, President Barack Obama said in his weekly address that there is "no greater threat to our planet than climate change."

"Climate change can no longer be denied or ignored," with 14 of the 15 hottest years on record happening in the first 15 years of this century, he said. Last year was the warmest recorded year.

The Earth's rising temperatures are having "very serious implications," the president said, including stronger storms, deeper droughts and longer wildfire seasons.

The U.S. leader said he would observe Earth Day on Wednesday at Florida's Everglades, a location he described as "one of the most special places in our country" and "one of the most fragile." He said rising sea levels are putting the "national treasure" at risk.

The world is looking to the U.S. to take a leadership role in dealing intelligently with climate change, Obama said. "And that's what we're doing," he said, adding that America is using more clean energy than ever before and is number one in wind power use. He said other measures taken include an increasing number of energy-efficient cars and buildings that save consumers money.